"TO packages" are commonly used for a variety of electronic and optoelectronic devices. A TO package has a circular metallic header having a lip on its outer circumference and a plurality of through holes spaced around its circumference. A terminal pin extends through each hole and is held in the hole and separated from the header by an insulating spacer. The TO package also has a cylindrical cap which fits onto the header with a circular edge of the cap mating with the lip of the header. In TO packages intended for use with optoelectronic devices, the cap has a transparent window which is located over the header when the cap is installed on the header. TO packages come in several TO-standard diameters with several TO-standard pin counts.
A surface-coupled optoelectronic device, such as a surface-emitting laser, a surface-emitting LED, or a surface-receiving photodetector is mounted in a TO package by securing to the header a substrate on which the device is formed, wire-bonding electrical connections from the terminal pins to contact pads on an upper surface of the device, mating the cap with the header, and sealing the cap to the header at the lip of the header. In the packaged device, the window of the cap is aligned with the surface of the device, so that the device can be optically coupled to external components through the window.
However, if an edge-coupled optoelectronic device, such as an edge-emitting laser, an edge-emitting LED or an edge-receiving photodetector were mounted in a TO package as described above for a surface-coupled optoelectronic device, the device would not be properly oriented for optical coupling through the window. The edge-coupled device must be mounted perpendicular to the header for optical coupling through the window.
The required perpendicular mounting is conventionally achieved by securing a block to the surface of the header, and securing the edge-coupled device to a lateral surface of the block. Electrical connections are wire-bonded to contact pads of the device but, because the wire-bonding surfaces of the terminal pins are perpendicular to the contact pads of the device when the device is mounted perpendicular to the header, the electrical connections cannot be wire-bonded to the terminal pins. Instead the electrical connections must be connected to the terminal pins with solder or conductive epoxy. Unlike wire-bonding which can be totally automated, the soldering or epoxying operation is performed manually. The cap is then fixed to the header with the window over the edge of the edge-coupled device.
The requirement for a manual soldering or epoxying operation significantly increases the production time and cost associated with the packaging of edge-emitting optoelectronic devices in TO packages.
Edge-coupled optoelectronic devices have also been mounted in "flat pack" or "butterfly" packages having optical connectors or optical fiber pigtails built into an end wall of the package for optical coupling to the edge-coupled device. In these packages, contact pads of the devices can be wire-bonded to terminal pins of the packages in an automated wire-bonding operation. However, these packages are several times more expensive than TO packages. Moreover, TO packages are standardized for many cost-sensitive applications and are compatible with readily available and inexpensive connector adaptors.
Thus, there is a need for a simpler method for mounting an edge-coupled optoelectronic device in a "TO-style" package and a need for a "TO-style" package adapted to such a method.